We posed this question to Pablo Päster, a Greenhouse Gas Engineer and Columnist for treehugger.com...Pablo - http://www.informationisbeautiful.net/ _blank>Informationisbeautiful.net actually did a great analysis of this and showed that the European aviation industry has about twice as many emissions[img float=right]/forum/copies/RTEmagicC_800px-Eyjafjallajokull_volcano_plume_2010_04_18.JPG.jpg[/img] as the volcano on a regular day. So the volcano has an estimated 150,000 metric tonnes of greenhouse gas emissions whereas the European aviation industry has 344,000 metric tons of greenhouse gas emissions. So, there’s actually over 200,000 tonnes saved per day by cancelling 60% of the flights across Europe. Volcanic greenhouse gas emissions are quite different from human greenhouse gas emissions in that, they have been coming out at a steady state over time whereas we are now artificially changing that balance so that the rate of emissions versus the rate of absorption has been accelerated or put out of balance. The US Environmental Protection Agency estimates that the global greenhouse gas emissions from human activities totalled 28 trillion metric tonnes in 2006, so that's put this volcano in some perspective. In 2008, the greenhouse gas emissions of oil company Chevron and power company AEP, exceeded the greenhouse gas emissions from volcanoes in that year. Diana - Even an enormous volcanic eruption cannot match the European aviation industry for carbon emissions. It’s thought that just over 200,000 tons of carbon dioxide per day where not emitted as a result of grounding 60% of the flights in and around Europe. With the volcano emitting 150,000 tonnes per day, it would mean that the volcano is better for the atmosphere by 50,000 tons of CO2 per day. On a few bad days, it’s estimated that Eyjafjallajokul emitted up to 300,000 tonnes of CO2 which would make it worse to the tune of 100,000 tonnes than the flights which would’ve otherwise been in the air.

I would hazard, that as the ash cloud stopped air travel throughout the EU, that there had to be a significant amount of gas emitted. If there was enough ash and such to signifigantly damage turbine engines that entered these clouds after they had dispersed over a long distance then the initial volume emitted into the upper atmosphere would have to be huge, certainly in the tens of thousands of ton range, or even much larger. AFAIK volcanoes emit amongst others CO2, water and a near lethal brew of gases, including a whole lot of sulphur, chlorine and flourine compounds, mostly very hot, and generally going almost directly to the stratosphere, along with a good amount of ash and rock. At a guess this amount of gas would be a lot more than that emitted by aviation during the same period, and would be a mixture with a lot more harmful effects.